Means and method for explosive forming materials at high temperatures



April 14, 1964 A. L. PAYNTER ETAL I 3,128,732

MEANS AND METHOD FOR EXPLOSIVE FORMING MATERIALS AT HIGH TEMPERATURES Filed Jan. 24. 1961 2 Sheets-Sheet 1 pi 2 INVENTORS 2 g ALLISON L. PAYNTER By CHARLES W. GIPE April 14; 1964 A. L. PAYNT-ER ETAL 3,128,732

MEANS AND METHOD FOR EXPLOSIVE FORMING f MATERIALS AT HIGH TEMPERATURES- Filed Jan. 24. 1961 ALLISON L. PAYNTER HARLES W. GIPE BY c 2 Sheets-Sheet 2' United States Patent Ofiiice 3,128,732 Patented Apr. 14., 1964 3,123,732 MEANS AND METHGD FOR EXPLOSIVE FORMENG MATERIALS AT HIGH TEMPERATURES Aliison Lloyd Paynter and Charles W. Gipe, San Diego,

Calif., assignors to The Ryan Aeronautical Co., San

Diego, (Zalif.

Filed Jan. 24, W61, Ser. No. 84,635 8 Claims. (Cl. 1l3-44) The present invention relates generally to metal forming and more particularly to a means and method for explosive forming materials at high temperatures.

Many high strength materials, such as titanium and various stainless steels, are difiicult to form by pressing or drawing and are satisfactorily shaped only by high energy forming using an explosive charge. Even with this method the results are not always as desired, since certain of the materials must be worked in their fully hardened condition, for various reasons and can be effectively formed only at elevated temperatures. In the conventional explosive forming operation, the blank material is clamped in a shaped die and immersed in a tank of water, an explosive charge being fired in the vicinity of the blank and the water serving as the pressure conducting medium to apply the explosive force to the blank, while protecting the material from the destructive aspects of the explosion. The material is always at ambient temperature due to the limitations of heating of the water. To form materials at high temperatures by explosive means, it is necessary to heat the part and the die and to use a pressure conducting medium which is heat resistant and of low thermal conductivity.

The primary object of this invention, therefore, is to provide a means and method for explosive forming materials in heated dies and applying the explosive force through a pressure conducting medium which retains the heat and effectively distributes the explosive force evenly to the blank being formed.

Another object of this invention is to provide explosive forming means using a pressure conducting medium of particulate form, such as alluvial sand, which flows readily under pressure yet is not damaged by the heat or explosion.

Another object of this invention is to provide explosive forming means in which the material being formed is maintained at the required temperature by controlled heated dies and the insulation of the initial layer of pressure conducting medium contact with the material, successive layers of the medium insulating the explosive charge from the heat and preventing premature firing.

A further object of this invention is to provide explosive forming means in which the material blank is held on the die by a clamp plate, also heated and incorporating a standpipe in which the pressure conducting medium is contained, the arrangement being adaptable to many types of dies.

Finally it is an object to provide an explosive forming means and method of the aforementioned character which is simple and convenient to use and which will give accurate and consistent results on a production basis.

With these and other objects definitely in view, this invention consists in the novel construction, combination and arrangement of elements and portions, as will be hereinafter fully described in the specification, particularly pointed out in the claims, and illustrated in the drawings which form a material part of this disclosure, and in which:

FIGURE 1 is a top plan view of the apparatus;

FIGURE 2 is a sectional view of the lower portion of the apparatus taken on the line 2-2 of FIGURE 1; and

FIGURE 3 is a sectional view, similar to FIGURE 2,

showing the complete apparatus set up for a forming op eration.

Similar characters of reference indicate similar or identical elements and portions throughout the specification and throughout the views of the drawing.

The apparatus comprises two major components, a die block 16 and a clamp plate 12 having an upright standpipe 14 fixed thereto. The die block 10 has a depression therein which will be referred to as the cavity 16, shaped to conform to the contours of the part to be formed, the configuration being adaptable to a wide range of forming and blanking dies, and is provided with a vent 18 communicating with a vacuum connection 20, so that the cavity can be evacuated. Surrounding the die block lib are a plurality of heating elements 22, the number and arrangement of the elements being suited to the par ticular die configuration to provide the desired heat distribution. The die block 16 is surrounded by an insulating jacket 24 of thermal insulating material and rests on an insulating pad 26 which, in turn, rests on a heavy base pad 28.

The clamp plate 12 is designed to cover the top of the die block 10 and has an opening 3i) at least equal in size to the opening of the cavity 16. The standpipe i4 is a cylindrical container, open at both ends and of suitable diameter to enclose the opening 30, said standpipe being fixed to the top of the clamp plate 12 by welding, or other such means, and having suificient strength to withstand an explosive charge fired therein. Recessed in the clamp plate 12 are heating elements 32, located to provide the desired heat distribution, the clamp plate being surrounded by an insulating jacket 34 and the top surface covered by an insulating ring 36 fitted around the standpipe M. The clamp plate 12 is illustrated as being attached to the die block 10 by cap screws 38, but any suitable bolts, clamps, or other fastening devices may be used.

In operation, the set-up steps of the process include placing a sheet of material or blank 4i which is to be formed, on top of the die block it) and secured by fastening the clamp plate 12 in place tightly. The process necessarily includes a conditioning step of heating. The

lank 40 may be preheated or can be heated in place in the fixture to the required temperature, which will vary according to the material being used. The heating elements 22; and 32 may be electrical resistance or induction type, hot gas conductors, or any other type according to the temperature range involved. The standpipe 14 is then substantially dium 4,2 in which is embedded an explosive charge 44, at a predetermined distance from the blank 41), the lower face of the column of pressure conducting medium being in direct contact with the upper face of said blank.

Since the apparatus is intended primarily for forming materials at high temperatures, the use of water, as in conventional explosive forming, is impractical as a pressure conducting medium. The material used must be capable of flowing freely under pressure to distribute force evenly over the entire working surface and must also be heat resistant to prevent decomposition from the continued heat of the die or the instantaneous heat of explosion. While certain types of oils or special fluids may be suitable for the lower temperature ranges, a solid, particulate material is more adapted to the specific needs. One material which has been found to be especially suitable is alluvial sand, having very small particles which are individually smooth and have no sharp edges which might damage the surface of the blank, the sand being heat resistant and of low thermal conductivity.

The high temperatures involved necessitate careful arrangement 0f the pressure conducting medium and the explosive charge in order to prevent premature firing of filled with a pressure conducting methe charge by the heat of the die assembly. In the preferred process, an initial layer 46 of the pressure conducting medium is poured onto the entire portion of the blank 40 exposed in the opening 30 of the clamp plate 12, this layer either being preheated or allowed to become heated to avoid undue cooling of the blank. A second layer 48 of cold, or ambient temperature pressure conducting medium is then poured on the first layer to serve as an insulation between the heated area and the explosive charge 44, which is then placed in position and buried in the remainder of the pressure conducting medium 42 substantially filling the standpipe 14. Various types of explosive charges may be used, singly or in multiple according to the size and shape of the part to be formed.

The cavity 16 is evacuated through the vacuum connection 20 to avoid air bubbles and the explosive charge 44 is fired, by means of a suitable firing cable 50. The explosion drives the pressure conducting medium 42 against the blank 40 and forces the blank into the shape of the cavity 16, the basic action and effectiveness of such high energy forming being well known. After the explosion the shaped part can be removed and cooled, the pressure conducting medium being emptied and stored for re-use. For convenience of handling, lifting lugs 52 may be fixed to the upper end of the standpipe 14.

The temperature of the die block and clamp plate 12 can be accurately controlled to maintain the blank 40 at a suitable working temperature without danger of inadvertently annealing the material. However, since such heat treatment processes involve time as well as temperature factors, the duration of heating involved will normally be too short to affect the material.

The die structure can be made in virtually any shape or size and, when properly designed, the apparatus may be used without the need for any protective shields, such as submerging the entire assembly in a tank or pit. By covering the explosive charge with an appropriate depth of the pressure conducting medium, the explosion is confined to the standpipe and dissipated throughout the particulate material, so that in normal use, none of the material will be ejected from the standpipe.

The use of heated dies and a heat resistant medium to contain the explosion combines the advantages of hot forming for ease of working certain materials, together with the advantages of explosive forming which is necessary to shape exceptionally hard metals and alloys virtually unworkable by previous methods. The apparatus is simple to construct and does not require a permanent installation, as with presses or the like capable of comparable work.

The operation of this invention will be clearly comprehended from a consideration of the foregoing description of the mechanical details thereof, taken in connection with the drawing and the above recited objects. It will be obvious that all said objects are amply achieved by this invention.

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

We claim:

1. Means for explosive forming materials at high temperatures, comprising: a die block having a cavity shaped to conform to the part to be formed; a clamp plate removably attachable to said die block to hold a blank to be formed over said cavity in sealed relation therewith; a plurality of heating elements operatively mounted in both said die block and said clamp plate; said clamp plate having an opening substantially corresponding in area with the mouth of said cavity; a standpipe fixed on said clamp plate above said opening, heated sand within said open ing and contacting the entire area of said part exposed in said opening thus assuring the heating of said entire area;

cool sand in said standpipe above said heated sand; said heated sand insulating said entire area of said part from said cool sand; an explosive charge embedded in said cool sand and thus protected from the heat of the hot sand and from the heat generated by said heating elements; and means for firing said explosive charge to drive the blank into said cavity.

2. Means for explosive forming materials at high temperatures, comprising: a die block having a cavity shaped to conform to the part to be formed; a clamp plate removably attachable to said die block to hold a blank to be formed over said cavity in sealed relation therewith; a plurality of heating elements operatively mounted in said die block and said clamp plate; said clamp plate having an opening substantially corresponding in area with the mouth of said cavity; an open ended standpipe fixed to said clamp plate and enclosing said opening; a heated particulate, pressure conducting medium contained in said standpipe and having contact with the blank; a cool particulate medium within said standpipe and on top of said heated particulate; an explosive charge embedded in said cool particulate medium; and means for firing said explosive charge, whereby the blank is driven into said cavity by pressure transmitted by said pressure conduct ing medium.

3. Explosive forming means according to claim 2, wherein said particulate pressure conducting medium is in layers including a hot layer covering said part; and a cool layer adjacent said explosive charge; said hot layer preventing cooling of the part by said cool layer, and said cool layer preventing thermal pre-detonation of said charge.

4. Explosive forming means according to claim 2, wherein said pressure conducting medium is alluvial sand in layers including a pre-heated layer contacting the entire surface of said part within said clamp plate; a cool layer on top of said pre-heated layer; said pre-heated layer preventing cooling of any portion of said part by said cool layer, and said cool layer preventing pre-detonation of said charge.

5. A method of explosive forming materials at high temperatures, comprising: the steps of clamping a blank over a depression in a die block, tightly holding a standpipe over the depression in the die block, placing in the standpipe a layer of hot particulate material on top of said blank, placing a layer of cool particulate material on top of said hot layer, embedding an explosive charge in said cool layer, and detonating the explosive charge.

6. A method for explosive forming materials at high temperatures, comprising: heating a die block having therein a cavity with a shape corresponding to the part to be formed; heating a clamp plate having an open ended standpipe fixed thereto; securing a blank of material between the die block and the clamp plate with the standpipe over the portion of the blank to be formed; placing a layer of hot particulate material within the standpipe and on top of the blank, placing a layer of cool particulate material on top of the hot layer; embedding an explosive charge in the cool layer; and firing the explosive charge to drive part of the particulate material against the blank and force the blank into the die block cavity.

7. A method for explosive forming materials at high temperatures, comprising: heating a die block having therein a cavity with a shape corresponding to the part to be formed; heating a clamp plate having an open ended standpipe fixed thereto; securing a blank of material between 'the die block and the clamp plate with the standpipe over the portion of the blank to be formed; applying over the blank an initial layer of hot particulate material to retain the heat in the blank; applying a second layer of cool particulate material over the initial layer; mounting an explosive charge in the standpipe, adjacent to and protected from the heat by the second layer; applying a further quantity of particulate material to embed the explosive charge; and firing the explosive charge to drive some of the particulate material against the blank and force the blank into the die cavity.

8. A method according to claim 7 wherein the particulate material used is sand.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,005 Middleton et a1. July 4, 1950 2,547,331 Lent Apr. 3, 1951 2,935,038 Chatten May 3, 1960 10 6 FOREIGN PATENTS 16,270 Great Britain Aug. 3, 1908 565,681 Great Britain Nov. 22, 1944 OTHER REFERENCES Explosive Forming, American Machinist, vol. 103, No. 12, June 15, 1959, pp. 127-138, 113-44E.

High Energy Rate Metal Forming, Interim Engineering Report No. 2, PB 161272, distributed by Ofiice of Technical Services, (OTS) U.S. Dept. of Commerce, Feb. 12, 1960, page 18, copy available in Div. 14, 113-44E. 

1. MEANS FOR EXPLOSIVE FORMING MATERIALS AT HIGH TEMPERATURES, COMPRISING: A DIE BLOCK HAVING A CAVITY SHAPED TO CONFORM TO THE PART TO BE FORMED; A CLAMP PLATE REMOVABLY ATTACHABLE TO SAID DIE BLOCK TO HOLD A BLANK TO BE FORMED OVER SAID CAVITY IN SEALED RELATION THEREWITH; A PLURALITY OF HEATING ELEMENTS OPERATIVELY MOUNTED IN BOTH SAID DIE BLOCK AND SAID CLAMP PLATE; SAID CLAMP PLATE HAVING AN OPENING SUBSTANTIALLY CORRESPONDING IN AREA WITH THE MOUTH OF SAID CAVITY; A STANDPIPE FIXED ON SAID CLAMP PLATE ABOVE SAID OPENING, HEATED SAND WITHIN SAID OPEN- 